Pox Immunization. 315 



few exceptions, by only a local and very mild pox eruption, and the 

 time for vaccination may be chosen according to convenience. The 

 unfavorable results which are observed in flocks suffering from natural 

 infection and the severe form which develops in unfavorable weather, 

 together with prolonged duration of the disease, may thereby be 

 eliminated. The vaccination of the animals therefore serves entirely 

 the purpose for which it is intended. 



The vaccine is the original, not attenuated virus of pox, which 

 continues to propagate in this highly virulent condition in the inoculated, 

 animal. As a result of this, flocks which have not been vaccinated are 

 threatened to a great extent by the vaccinated animals, and particularly 

 so as the resulting infection usually appears generalized, and fre- 

 quently causes a malignant eruption of pox. If the vaccination were 

 carried out from year to year on all sheep of a country all subsequent 

 infection of the native animals could be excluded; since however vac- 

 cination is practiced only in certain localities, and there mostly in 

 single flocks, every vaccinated herd represents annually reproduced 

 artificial infection, from which the artificially propagated virus may 

 sometimes become disseminated and produce severe outbreaks of pox. 



Considered from a general viewpoint the vaccination of lambs 

 is therefore positively harmful, especially as the location of the flocks 

 is but rarely changed, and they may be easily protected against the 

 infection by safer measures. 



Observations on this point made in Germany aiford convincing proof. Since 

 1875 the vaccination in Prussia has been dependent upon official permits. This 

 resulted immediately in a conspicuous reduction of pox, and consequently the 

 Imperial law on animal diseases in 1818 prohibited vaccination except in emergency 

 eases. The results came up to expectations, inasmuch as Germany has been almost 

 entirely free from the disease since that time. Pox has appeared from time to 

 time, owing to importations from foreign countries, but in all instances the disease 

 has been controlled and limited to the primarily affected flocks. In Austria a 

 law was passed in 1880 by which the vaccination was permitted only with official 

 sanction, and this also resulted in a striking reduction of the disease. On the 

 other hand in France, Hungary, and in the eastern and southern European countries 

 where vaccination is still in vogue, considerable loss from pox results from year to 

 year among the sheep. 



TecIiniqLue of the Vaccination. The clear, yellowish, or yellowish-red, serous 

 contents of the ripe vesicle which is obtained from young vigorous sheep, in which 

 the eruption develops only in moderate extension and in association with only 

 slight febrile symptoms is used as vaccine. The vaccine should never be taken 

 from a purulent vesicle, and is still more dangerous if it originates from animals 

 in which ^le papules have coalesced, or in which the presence of hemorrhages 

 indicate a severe character of eruption. At the beginning of an outbreak it is 

 advisable to vaccinate only a few sheep from the first affected animals, and then 

 from these the lymph should be taken for the remaining part of the flock. In 

 such cases the lymph may be taken ten to twelve days after vaccination, otherwise 

 in from 5 to 7 days after the appearance of the eruptions. If however lymph 

 from the animals vaccinated the previous year is available it is best to use such 

 for the vaccination. 



The contents of the ripe vesicle are collected in capillary tubes. The tubes 

 are previously heated, and one end of the tube is stuck into the vesicle. In an 

 emergency however the lymph may be collected from an open vesicle in glass bottles. 

 It is less advisable to utilize the scabs which develop at the place of the vesicles 

 for the vaccination. Vaccinations may also be carried out directly from animal to 

 animal by first inserting the vaccination instrument in the vesicle, and then im- 

 mediately into the skin of the animal to be vaccinated. Serous fl.uid obtained by 

 squeezing incised nodules may be also utilijed for vaccine. 



The most favorable place for vaccination is the under surface of the tail 

 •which is free from wool, 5-10 cm. from the rectum, or the inner surface of 

 the ear 3-4 cm. below its point. Less suitable is the inside of the thigh, the scrotum 

 and the abdominal region. As instruments, the vaccinating lancet or still better 



